Jared T. Shaw

Chemical inhibition of the mitochondrial division dynamin reveals its role in Bax/Bak-dependent mitochondrial outer membrane permeabilization

Mitochondrial fusion and division play important roles in the regulation of apoptosis. Mitochondrial fusion proteins attenuate apoptosis by inhibiting release of cytochrome c from mitochondria, in part by controlling cristae structures. Mitochondrial division promotes apoptosis by an unknown mechanism. We addressed how division proteins regulate apoptosis using inhibitors of mitochondrial division identified in a chemical screen. The most efficacious inhibitor, mdivi-1 (for mitochondrial division inhibitor) attenuates mitochondrial division in yeast and mammalian cells by selectively inhibiting the mitochondrial division dynamin. In cells, mdivi-1 retards apoptosis by inhibiting mitochondrial outer membrane permeabilization. In vitro, mdivi-1 potently blocks Bid-activated Bax/Bak-dependent cytochrome c release from mitochondria. These data indicate the mitochondrial division dynamin directly regulates mitochondrial outer membrane permeabilization independent of Drp1-mediated division. Our findings raise the interesting possibility that mdivi-1 represents a class of therapeutics for stroke, myocardial infarction, and neurodegenerative diseases.

Recent advances in multicomponent reactions for diversity-oriented synthesis

Interest in multicomponent reactions (MCRs) has surged during the past two decades as interest in the efficient synthesis of small molecule libraries has gained prominence. MCRs fill an important niche in library synthesis by providing direct access to library compounds and by serving as starting points for Diversity-Oriented Synthesis (DOS). Recent advances in the area of MCR chemistry have included the discovery of new reactions, development of the first asymmetric catalysts, and the application of MCRs to natural products and other targets of biological interest. This review will highlight recent developments in MCRs as a rich source of molecular diversity.

Cyclic Anhydrides in Formal Cycloadditions and Multicomponent Reactions

The reactions of cyclic anhydrides acting dually as acylating agents and C-nucleophiles in stereoselective annulation reactions provide efficient one-step synthesis of polysubstituted heterocyclic and carbocyclic molecules. The reactivity of anhydrides is historically dominated by their ability to serve as mild acylating agents. An early example of anhydrides acting as C-nucleophiles is found in the Perkin reaction, in which aliphatic anhydrides undergo aldol condensation with aldehydes in the presence of a mild base (eq 1). An early report of the reaction of homophthalic anhydride with an aldehyde (eq 2) using strong base demonstrated the ability for cyclic anhydrides to undergo annulation reactions. Castagnoli observed in 1969 that cyclic anhydrides undergo formal cycloaddition reactions with imines (eq 3) under thermal conditions. This discovery, paired with the observations of Cushman and Haimova (eq 4) in 1977 that homophthalic anhydride underwent a similar reaction at ambient temperature, formed the foundation for much of the subsequent work on this reaction. Finally, Tamura reported a related transformation in which homophthalic anhydride reacted with alkenes and alkynes to produce fused aromatic products (eq 5).

The Correct Structure of Aquatolide—Experimental Validation of a Theoretically-Predicted Structural Revision

Aquatolide has been reisolated from its natural source, and its structure has been revised on the basis of quantum-chemical NMR calculations, extensive experimental NMR analysis, and crystallography.

Enantioselective intramolecular C-H insertion reactions of donor-donor metal carbenoids

The first asymmetric insertion reactions of donor–donor carbenoids, i.e., those with no pendant electron-withdrawing groups, are reported. This process enables the synthesis of densely substituted benzodihydrofurans with high levels of enantio- and diastereoselectivity. Preliminary results show similar efficiency in the preparation of indanes. This new method is used in the first enantioselective synthesis of an oligoresveratrol natural product (E-δ-viniferin).

Comparison of small molecule inhibitors of the bacterial cell division protein FtsZ and identification of a reliable cross-species inhibitor.

FtsZ is a guanosine triphosphatase (GTPase) that mediates cytokinesis in bacteria. FtsZ is homologous in structure to eukaryotic tubulin and polymerizes in a similar head-to-tail fashion. The study of tubulins function in eukaryotic cells has benefited greatly from specific and potent small molecule inhibitors, including colchicine and taxol. Although many small molecule inhibitors of FtsZ have been reported, none has emerged as a generally useful probe for modulating bacterial cell division. With the goal of establishing a useful and reliable small molecule inhibitor of FtsZ, a broad biochemical cross-comparison of reported FtsZ inhibitors was undertaken. Several of these molecules, including phenolic natural products, are unselective inhibitors that seem to derive their activity from the formation of microscopic colloids or aggregates. Other compounds, including the natural product viriditoxin and the drug development candidate PC190723, exhibit no inhibition of GTPase activity using protocols in this work or under published conditions. Of the compounds studied, only zantrin Z3 exhibits good levels of inhibition, maintains activity under conditions that disrupt small molecule aggregates, and provides a platform for exploration of structure-activity relationships (SAR). Preliminary SAR studies have identified slight modifications to the two side chains of this structure that modulate the inhibitory activity of zantrin Z3. Collectively, these studies will help focus future investigations toward the establishment of probes for FtsZ that fill the roles of colchicine and taxol in studies of tubulin.

Inhibitors of bacterial tubulin target bacterial membranes in vivo

FtsZ is a homolog of eukaryotic tubulin that is widely conserved among bacteria and coordinates the assembly of the cell division machinery. FtsZ plays a central role in cell replication and is a target of interest for antibiotic development. Several FtsZ inhibitors have been reported. We characterized the mechanism of these compounds in bacteria and found that many of them disrupt the localization of membrane-associated proteins, including FtsZ, by reducing the transmembrane potential or perturbing membrane permeability. We tested whether the reported phenotypes of a broad collection of FtsZ inhibitors disrupt the transmembrane potential in Bacillus subtilis strain 168. Using a combination of flow cytometry and microscopy, we found that zantrin Z1, cinnamaldehyde, totarol, sanguinarine, and viriditoxin decreased the B. subtilis transmembrane potential or perturbed membrane permeability, and influenced the localization of the membrane-associated, division protein MinD. These studies demonstrate that small molecules that disrupt membrane function in bacterial cells produce phenotypes that are similar to the inhibition of proteins associated with membranes in vivo, including bacterial cytoskeleton homologs, such as FtsZ. The results provide a new dimension for consideration in the design and testing of inhibitors of bacterial targets that are membrane-associated and provide additional insight into the structural characteristics of antibiotics that disrupt the membrane.

Ammonia synthons for the multicomponent assembly of complex γ-lactams

The synthesis of γ-lactams that are unsubstituted at the 1-position (nitrogen) as well as their subsequent N-functionalization is reported. A recently discovered four-component reaction (4CR) is employed with either an ammonia precursor or a protected form of ammonia that can be deprotected in a subsequent synthetic step. These methods represent the first multicomponent assembly of complex lactam structures that are unsubstituted at nitrogen. In addition, two methods for the introduction of nitrogen substituents that are not possible through the original 4CR are reported. X-ray crystallographic analysis of representative structures reveals conformational changes in the core structure that will enable future deployment of this chemistry in the design and synthesis of diverse collections of lactams suitable for the discovery of new biological probes.

Zinc-Catalyzed Silylation of Terminal Alkynes

A rapid and high-yielding silylation of terminal alkynes employing TMSOTf and catalytic quantities of Zn(OTf)2 has been developed. The reaction works well for a variety of substrates including reactive esters. Fifteen examples with yields of >90% are reported.

Stereocontrol in Asymmetric γ-Lactam Syntheses from Imines and Cyanosuccinic Anhydrides

Computations (SCS-MP2//B3LYP) reveal that the asymmetric synthesis of highly substituted γ-lactams with three stereogenic centers, including one quaternary center, proceeds through a Mannich reaction between the enol form of the anhydride and the E-imine, followed by a transannular acylation. This new mechanistic picture accounts for both the observed reactivity and stereoselectivity. CH-O and hydrogen bonding interactions in the Mannich step and torsional steering effects in the acylation step are responsible for stereocontrol. It is demonstrated that this new mechanistic picture applies to the related reactions of homophthalic anhydrides with imines and presents new vistas for the design of a new reaction to access complex molecular architectures.